Electroscopic particle sensor



March 4, 1969 D. L. PEASE ET AL 3,430,606

ELECTROSCOP I C PARTICLE SENSOR Filed Jan. 2, 1968 I I II II HI INVENTORS DONALD L. PEASE HENRY A.TWIST 1 ATT/PNEYS.

March 4, 1969 Filed Jan. 2/ 1968 D. I... PEASE E ELECTROSCOPIC PARTICLE SENSOR I AT INVENTORS DONALD L. PEASE HENRY A.TWlST o/wvers March 4, 1969 D. L. PEASE ET AL ELECTROSGOPIC PARTICLE SENSOR Sheet Filed Jan. 2, 1968 FIG. 3

i .nllllHlM INVENTORS DONALD L. PEASE HENRY A. TWIST 6 Claims ABSTRACT OF THE DISCLOSURE Apparatus for monitoring the density of electroscopic toner powder images wherein electrically conductive light transmissive electrodes are utilized as a xerographic photoreceptor simulator for cyclically developing and cleaning a toner powder image on the electrode surface and sensing the density thereof at a predetermined time by passing a light beam through the electrodes and developer material into a photosensor.

Background of the invention This invention relates to xerographic development and in particular to a novel xerographic photoreceptor simulator adapted to monitor the concentration of electroscopic toner powder in a xerographic developer mixture.

More specifically, the invention relates to a photoreceptor simulator utilizing an electrically conductive light transmissive electrode for monitoring the toner powder in a dynamic xerographic developer system. The electrodes are utilized for cyclically developing and cleaning a toner powder image on the electrode surface and sensing the concentration of electroscopic toner powder in xerographic developer material at a predetermined time.

In the process of xerography, a Xerographic plate comprising a layer of photoconductive material on a conductive backing is given a uniform electric charge over its surface and then exposed to the subject matter to be reproduced by various projection techniques. This exposure dicharges the plate in accordance with the light intensity reaching it, thereby creating a latent electrostatic image on or in the plate.

Development of the image is effected by developers which comprise, in general, a mixture of suitable pigmented or dyed resin-based powder, hereinafter referred to as toner, and a granular carrier material which functions to generate tri boelectric charges on, and to carry the toner. More specifically, the function of the carrier material is to provide mechanical control of the toner, or to carry to an image surface and simultaneously provide almost complete homogeneity of charge polarity. In the development of the image, the toner powder is brought into surface contact with the photoconductive coating and is held thereon electrostatically in a pattern corresponding to the latent electrostatic image. Thereafter, the developed xerographic image may be transferred to a support material to which it may be fixed by any suitable means such as heat fusing.

In the mixture of toner particles and carrier material, the toner particles, which are many times smaller than the carrier material, adhere to and coat the surface of carrier material due to the triboelectric attraction therebetween. During development, as the toner-coated carrier material rolls or tumbles over the xerographic plate carry- United States Patent ing an electrostatic image of opposite polarity to the charge on the toner, toner particles are pulled away from the carrier by the latent electrostatic image and deposited on the plate to form a developed toner-powder image. As toner-powder images are formed, additional toner powder must be supplied to the developer mixture to replenish the toner deposited on the xerographic plate. The toner material may be of the type disclosed in Carlson Patent No. 2,940,934, wherein the toner particles comprise a finely divided pigmented resin having a particle size less than 20 microns and preferably an average particle size between about 5 and 10 microns and comprising a finely divided uniform mixture of pigment in a non-tacky, low-melting resin. Desirably, the pigment will be a black pigment such as carbon black or other minutely divided carbonaceous pigment.

As the toner powder in the developer mixture is depleted during the development of the latent image on the xerographic plate, more toner powder must be added to maintain a desirable level of copy density. In the event that too much toner powder is added to the developer rnixture, heavy deposits of toner in the image areas in combination with an undesirable deposit of toner in the non-image or background areas results in producing prints of poor contrast with blotchy images or poor resolution.

In addition, overtoning by the operator adds to the severity of toner powder accumulation on critical machine components such as the corotrons, illumination system, optical system, fuser and transport system, as well as necessitating more frequent replacement of filter bags and cleaning brushes. Thus, with an automatic toner-powder control system incorporated in a xerographic machine to regulate the concentration of toner powder in the developer mixture, fewer service calls are necessary to keep the quality of the xerographic reproductions at a high level.

In automatic reproducing machines such as shown in FIG. 1 a moving xerographic plate, which may be in the form of a cylinder, is exposed to a light source to create a latent electrostatic image to be developed by appropriate :means such as a continuous flow of developer material over the plate surface. It is necessary, in order to produce prints of consistently good copy density, to vary the toner dispensing rate in accordance with the rate of consumption which is correlated to the type and frequency of copy being reproduced. The dispensing of toner in prior art devices has been dependent upon the machine operator visually inspecting the finished copy and manually adjusting for the toner concentration by appropriate changes in a machine setting. It is readily apparent that dispensing by this means results in image densities largely dependent on the alertness and ability of the operator to visually evaluate the density of the copy image. Not only must the operator detect the need for a setting change, but the operator must be able to accurately effect the proper degree of change through the dispenser setting. In the event that the operator oversets the dispensing rate and excess toner is added to the developer mixture, the only means whereby the toner concentration may again become acceptable is through normal depletion by reproduction of a sufficient number of additional copies. Considerable Waste of material and time usually occurs when the proper setting of toner concentration has to be determined by an operator, since setting changes are usually made only after copy deterioration has become apparent.

Various attempts have been made to develop a toner powder sensor which would simulate the development of a toner powder image on the photoreceptive surface of the xerographic plate or drum. It has been found that sensors which expose and develop a toner powder test image on a portion of the xerographic drum for use in determining the amount of toner powder in the xerographic developer material cause fatigue of the photoreceptive material and eventually give erroneous determinations of toner powder concentration. In an attempt to overcome the above problem apparatus was developed to simulate the photoreceptive surface of the xerographic drum. Such an apparatus is disclosed in U.S. Patent No. 3,694,049 issued June 18, 1963, to Christopher Snelling. The apparatus disclosed in the aforementioned patent determines the concentration of toner powder by comparing the amount of toner attracted to an electrode with fixed graduations marked thereon. Since the density of the image reproductions is the parameter which is desired to be controlled, a more desirable sensor would simulate the photoreceptor of the automatic xerographic reproducing machine and control the concentration of the toner powder in the developer mixture in relation to the density of toner powder image developed on the simulator surface.

Summary of the invention It is, therefore, an object of this invention to improve xerographic developing.

Another object of this invention is to improve xerographic developing by automatically adjusting the concentration of toner powder in the developer mixture in response to the density of a developed image.

A further object of this invention is to improve xerographic developing by cyclically developing and cleaning an electroscopic toner powder image on a xerographic drum simulator.

These and other objects are attained in accordance with the present invention wherein there is provided a xerographic drum simulator including transparent electrically conductive material positioned in cooperative relationship with the developer mixture of a xerographic reproducing machine and adapted to develop and clean an electroscopic toner powder image by means of the moving quantity of developer material. The simulator apparatus disclosed herein is adapted to provide a control signal in response to image density and is compensated for mechanical and electrical noise.

Description of the drawings Further objects of this invention together with additional features contributing thereto and advantages accruing therefrom, .will be apparent from the following description of one embodiment of the invention when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a front elevation view of an automatic xerographic reproducing machine utilizing the invention of this application;

FIG. 2 is an enlarged front elevation of the developer apparatus of the automatic xerographic reproducing machine with parts broken away to better illustrate the sensor apparatus of this invention;

FIG. 3 is an enlarged section view of the sensor chamber and electrodes;

FIG. 4 is a sectional view of the sensor chamber and electrodes taken along lines 4l of FIG. 3;

FIG. 5 is a sectional view of the simulator taken along lines 5--5 of FIG. 3; and,

FIG. 6 is an electrical schematic of the simulator apparatus.

Referring now to the drawings, there is shown in FIG. 1 an embodiment of the subject invention in a suitable environment such as an automatic xerographic reproducing machine, although it should be noted that the invention is not intended to be limited thereto.

Cit

The automatic xerographic reproducing machine includes a xerographic plate 1 including a photoconductive layer or light receiving surface on a conductive backing, journaled in a frame to rotate in the direction indicated by the arrow to cause the plate surface to sequentially pass a series of xerographic processing stations.

For the purpose of the present disclosure, the several xerographic processing stations in the path of movement of the plate surface may be described functionally, as follows:

A charging station 2 at which a uniform electrostatic charge is deposited on or in the photoconductive plate;

An exposure station 3 at which a light or radiation pattern of copy to be reproduced is projected onto the plate surface to dissipate the charge in the exposed areas thereof to thereby form a latent electrostatic image of the copy to be reproduced;

A developing station 4 at which the xerographic developing material, including toner particles having an electrostatic charge opposite to that of the latent electrostatic image is cascaded over the plate surface whereby the toner particles adhere to the latent electrostatic image to form a toner-powder image in configuration of the copy being reproduced;

A transfer station 5 at which the toner powder image is electrostatically transferred from the plate surface to a transfer material or a support surface; and

A drum cleaning and discharge station 6 at which the plate surface is brushed to remove residual toner particles remaining thereon after image transfer, and exposed to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining thereon or therein.

Description of the preferred embodiment It is felt that the preceding description of the xerographic process is sufficient for a better understanding of this invention. Referring now to the subject matter of the invention as best shown in FIGS. 1 and 2, the developing station which effects development of the latent electrostatic image of the cylindrical xerographic plate, comprises a developer apparatus 20 which coacts with the cylindrical plate to develop the latent electrostatic image on or in the plate surface by means of the xerographic toner-powder. Mounted within the developer housing is a driven bucket-type conveyor 210 used to carry the developer material previously supplied to the developer housing to the upper portion of the developer housing from which point the developer material is cascaded over the 'hopper chute 216 onto the drum. As the developer material cascades over the drum, toner particles of the developer material adhere electrostatically to the previously formed latent electrostatic image areas on the drum 1, the remaining developer material falling off the peripheral surface of the drum to be deflected by bathe plates 217 into the bottom of the developer housing. Toner particles consumed during the developing operation to form the visible powder images are replenished by a toner dispenser 10 mounted within the developer housing.

Specifically, the developer assembly 20 includes the box-like developer housing having a top wall 201, angular bottom wall 202, a front wall (not shown) and rear wall 204, forming in the lower portion thereof a reservoir for developing material. The front wall and rear wall 204 (as shown in FIG. 2) are formed with a concave edge portion in conformity with the shape of the xerographic drum to permit the developer housing to be positioned closely adjacent thereto. Secured to the inside faces of the developer housing are suitable bafile plates, not shown, which prevent excessive dust and air currents from circulating within the developer housing adjacent to the cylindrical xerographic plate.

The bucket-type converter 210 is used to convey developer material from the reservoir portion of the developer housing to the upper portion of the developer housing from where it is cascaded over the xerographic drum. As shown, the conveyor 210 includes a series of parallel spaced buckets 205 secured to a suitable pair of conveyor belts 206 passing around a conveyor drive pulley 207 and a conveyor idler pulley 208 secured on appropriate drive and idler shafts to rotate therewith.

To deflect the developing material and to spread this material across the face of the drum as the developing material is emptied out of the conveyor buckets by gravity, a flanged hopper chute 216 is secured as by welding to the side walls of the developer housing. As the xerographic drum rotates, developing material previously tumbled over the flanged hopper chute onto the drum from the buckets will cascade over the drum and eventually fall off or be thrown off the drum surface. To catch the developing material that falls from the Xerographic drum so that it may be returned to the reservoir in the developer housing, a pick-off bafile 217 is secured to the bottom wall 202 of the developer housing. The leading edge of the pick-off bafiie 217 is positioned closely adjacent to the peripheral surface of the Xerographic drum but out of contact therewith to catch the developing material as it falls from the drum surface. Any developing material not caught and returned to the reservoir of the developer housing by the pick-off baffie is caught by a pan (not shown) held in place by any suitable means secured to the bottom wall 202 of the developer housing. As a supply of developing material accumulates in this pan it must be manually removed by an operator and returned to the developer housing. For further details concerning the specific details of construction for a suit able developer apparatus reference is made to W. G. Lewis et al. US. Patent No. 3,067,720.

As the developing mixture is cascaded over the Xerographic drum, toner particles are pulled away from the carrier and deposited on the drum to form toner-powder images, while the partially denuded carrier particles pass off the drum into the reservoir. As toner powder images are formed, additional toner particles must be supplied to the developing mixture in proportion to the amount of toner deposited on the drum. To supply additional toner particles to the developing mixture, the toner dispenser is used to accurately meter toner to the developer mixture. Although any one of a number of wellknown powder or granulated material dispensers may be used, the toner dispenser shown (FIG. 2) is of the type disclosed in US. Patent No. 3,013,703, issued Dec. 19, 1961, to R. A. Hunt.

The toner dispenser 10 comprises a hopper or container 120 for the toner particles to be dispensed. Although the hopper or container 120 may be made in any size or shape, the hopper shown is formed as a rectangular openended box having vertical side and end walls, the upper ends of the walls being outward to form horizontal flanges by means of which the hopper may be attracted to the underside of top wall 201 of the developer housing, as by welding, with the opening in top wall 201 of the developer housing in alignment with the opening in the hopper. At opposite ends of the hopper are positioned depending bearing blocks for supporting the remaining elements of the toner dispenser, the bearing blocks being appropriately attached to the end walls.

The bottom of the hopper is partially closed by a dispensing plate positioned in spaced vertical relation below the lower edges of the walls of the hopper which combines with the walls of the hopper 120 to provide a reservoir having narrow elongated outlet slits or passages for the flow of toner powder. In the operation of the toner dispenser a supply of toner powder is placed within the hopper, the hopper walls and the dispensing plate forming a reservoir for the toner particles. Upon reciprocation of the dispensing plate, a metered quantity of toner powder will be permitted to pass through the It is felt that the preceding description of the toner dispenser 10 is sufficient for a better understanding of the subject matter of this invention. For further details relative to the specific construction of this device, reference is made to the aforementioned Hunt patent.

In order to control the dispensing of toner from the toner dispenser 10, there is shown in FIGS. 26 the details of a xerographic drum simulator which ultimately effectuates energization of the dispensing motor MOT-1 in accordance with the density of an image developed therein.

The Xerographic drum simulator, to be hereinafter described in detail, is secured within the developer housing 20 by suitable brackets which electrically insulate the simulator chamber from the surrounding structure. A collecting funnel 310 having depending side portions 311 adapted to contain a quantity of xerographic developer material is secured to support plate 312 fastened to the front and rear developer housing frame plates for main taining the collecting funnel, and simulator chamber 300 secured thereto, beneath the moving buckets 204 of the conveyor system to receive the overflow of developer material falling from each bucket as it progresses to cascade the developer material onto the xerographic plate. The collecting funnel 310, as shown in FIG. 2, is positioned at an angle relative to the vertical in such a way as to catch the falling developer material and to guide the material into the simulator apparatus 300.

The simulator apparatus 300 (FIGS. 3-5) includes photoelectric sensor P-1 and P-2 positioned in the path of light eminating from lamp LMP1 to vary the resistance of the sensors P-ll and P2 in proportion to the light intensity impinging thereon. Photosensor P1 is positioned adjacent lamp LMP-l to compensate for any variations in the light intensity due to lamp aging, line voltage variation, or toner dust accumulation Within the simulator apparatus. The two photosensors P-1 and P-2 are electrically connected in a bridge circuit whereby the changes in resistance of the photosensors are interpreted as changes in voltage, to thereby compensate the output voltage from the photosensor P2 for the above variations. Interposed in the light path eminating from lamp LMP1 to photosensor P-2, are a pair of electrically conductive transparent electrodes 350 each divided into two electrically isolated adjacent areas 350(a) and 350(b) for charging each of the areas of the electrodes to a desired polarity. A suitable type of electrode would be tin-oxide coated glass plate manufactured by Pittsburgh Plate Glass Inc. under the tradename of NESA Glass. Each of the electrically conductive surfaces of electrodes 350 are covered by a transparent glass plate 351 to protect the conductive surface from physical abrasion by the impacting developer material and to prevent the two adjacent electrically isolated areas 350(a) and 350(k) from shortening together when the apparatus is subjected to conditions of high relative humidity. The transparent electrodes are secured in posit-ion within the simulator chamber 301 by means of a spring 302 biasing the electrodes against a boss portion of the simulator chamber and are sealed in this position by a suitable sealant for a purpose to be hereinafter discussed. The simulator chamber comprises a hollow sealed member having an orifice in the upper portion through which the overflow of xerographic developer material is passed by means of the collecting funnel 310, the orifice being of a size such that a quantity of developer material is maintained in the collecting funnel at all times during operation of the developer apparatus 29. Positioned within the simulator chamber 3M adjacent the control orifice, is a flow divider 303 for diverting an equal amount of xerographic developer material over each of the transparent electrically conductive electrodes 35%. The flow divider 303 is electrically conductive and connected to machine ground. The grounding of flow divider 3E3 prevents the flowing developer material from building a static charge thereon which affects the triboelectric band between the carrier material and the toner powder. It has been found that the grounding of the flow divider 383, thereby increases the reliability of the simulator apparatus 360. If the flow divider is not grounded, the toner powder sometimes becomes more tightly bonded to the carrier material due to the static charge which builds up on the flow divider surface. When the triboelectric bond increases, less toner powder is attracted to the electrode surface which results in a false indication of a depleting concentration of toner powder in the developer mixture. As a result of grounding the flow divider, the static charge is dissipated and the tribeoelectric bond between the toner powder and carrier material is not altered by passing over the flow divider and erratic signals from the simulator are eliminated.

After the xerographic developer material has passed over the transparent electrodes, it flows out from the xerographic drum simulator through an aperture 3% in the bottom of the simulator chamber 301 to return to the sump portion of the developer housing 20. The purpose of the xerographic drum simulator being a sealed unit, except for the path of developer material flowing through the control orifice in the top of the simulator chamber and cascading over the transparent electrodes and out of the simulator, is to preclude the normal toner powder dust atmosphere within the developer housing 2t) from depositing on the photosensors P1 and P2 or the lamp LMP1. With the xerographic drum simulator being positioned and constructed in this manner, the same xerographic developer mixture that is being delivered to the Xerographic drum for development of the latent electrostatic image is utilized as a sample which is cascaded across the transparent electrodes, which simulate the photoreceptive drum, in the same manner as the developer mixture is applied to the drum surface. The two transparent electrically conductive electrodes have similar electrically isolated adjacent conductive areas 35tt(a) and SSMZJ) as best shown in FIG. 4. The patterns describing the conductive areas 350(a) and 356(1)) of each electrode are similar with areas 350(0) being electrically connected to terminal 15 and areas 350(1)) being electrically connected to terminal it) of the electrical schematic shown in FIG. 6 to which a suitable DC potential is applied.

The two electrodes 358 are electrically connected in parallel and coupled to a control circuit (Method and Controller for Dispensing Electroscopic Material, Ser. No. 695,244 filed currently herewith in the names of Ward R. Goodrich and Francis D. Witinski) whereby the polarity of the adjacent electrically isolated portions 359W) and 350(1)) is cyclically alternated to attract and repel toner powder from the xerographic developer material. Since the two adjacent but electrically isolated portions of the electrodes 350 are charged to opposite polarities, the greatest electrostatic field is created across the etched lines on each electrode (FIGURE 3). Therefore, the potential difference across the etched lines develops an image analogous to the latent image on the photoreceptive surface or Xerographic drum of the automatic xerographic reproducing machine, in that the toner powder particles are attracted to the area of greatest potential difference. When the polarity of the two electrodes is reversed this etched pattern provides a charge which repels the xerographic toner powder which is thereby cleaned by means of the continuous cascade of developer material across the electrode surface. This cleaning of the electrode surface by reversing the polarity, and thereby the potential across the etched lines of the electrically isolated portions of the transparent electrodes, is analogous to the cleaning method previously explained with reference to the photoreceptive drum.

The two electrodes are positioned in the sensor chamber 391 such that the light beam from lamp LMP-l passes most directly through the portion 358((1) of both electrodes. When the electrical charge on 350(12) is opposite to that of the toner powder, a toner powder image will be developed as the xerographic developer material cascades across the electrode surface. When the voltage on the electrode is cyclically reversed, the toner powder on the electrode surface in portion 350(a) will be repelled and this area of the electrode will be cleaned by the scrubbing action of the developer material continuing to cascade across the electrode surface. In this manner a toner powder image is periodically developed and cleaned from the test surface.

At a predetermined time as controlled by the electrical circuit disclosed in the aforementioned copending application, the dcnsity of the toner powder image attracted to the test area 350((1) is sensed by means of the light beam from lamp LMP-ll passing through the test portion of the electrodes and into photosensor P2. As shown in FIG. 6, the photosensor P-Z is connected into a bridge circuit with compensating photosensor Pll whereby the unbalanced output from the bridge is proportioned to the density of the toner powder attracted from the developer material to the electrode surface. Due to the cyclic variation of the electrical charge on the electrodes the output rom the bridge circuit will rise and fall generating an essentially saw-toothed waveform. This output from the bridge circuit is then coupled into the heretofore mentioned controller circuit whereat it is coupled to a threshold detector for energizing the toner powder dispenser motor MOT-1 for adding additional toner to the developer material as image density decreases.

While the invention has been described with reference to its preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof Without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teaching of the invention without departing from its essential teachings.

What is claimed is:

1. An electroscopic toner powder image density sensor including means defining a chamber for passing xerographic developer material therethrough,

a flow divider positioned within said chamber defining means to divide the passing developer material into a plurality of flow paths,

a plurality of light transmissive electrodes each of said plurality positioned adjacent one of said flow paths and in contact with passing developer material,

means to cyclically vary the voltage level on said electrodes for alternately developing and cleaning a toner powder image from the surface thereof, and

sensing means responsive to the density of the toner powder image developed on the electrode surface operatively connected to said electrodes for generating an electrical signal as a toner powder image is cyclically developed and cleaned from the electrode surface.

2. The apparatus of claim 1 wherein said flow divider comprises a grounded electrically conductive material.

3. The apparatus of claim 1 wherein each of said plurality of electrodes is positioned to intercept the passing developer material to effectuate a cascading of the developer material over the electrode surface.

4. The apparatus of claim 1 including means to retain a controlled amount of xerographic developer material for introduction into said chamber defining means at a predetermined flow rate.

5. The apparatus of claim 1 wherein said sensing means includes illuminating means positioned to direct a light beam through said electrodes and developer material, and a photosensor positioned in the light beam of said i1- luminating means with said plurality of electrodes and passing developer material therebetween. 6. The apparatus of claim 5 wherein said photosensor comprises an element of a bridge circuit including a second photosensor positioned adjacent said light beam prior to its passing through said electrodes and developer material to balance said bridge circuit for fluctuations in said light beam.

References Cited UNITED STATES PATENTS 3,094,049 6/1963 Snelling 118-637 XR 3,233,781 2/1966 Grubbs 22257 3,376,854 4/1968 Kamola 118637 

